Catfish live haul truck with aluminum tanks Portable submersible 12v pump used for filling tanks Diffuser hose grid attached to airlines and a slide gate installed in a fiberglass hauling tank. 4 2 MARCH 2007 as excessive mortality may occur. Fish recently treated with antibiotics must be held in the pond for the proper withdrawal period before they are sold for human consumption. Fish health records should be made available to customers before the fish are transported from the farm. Table 2 provides loading rates for catfish of different sizes. In some instances, the weight of fry and small fingerling catfish, in addition to other fish species, may be determined by volumetric water displacement using calibrated hauling tanks during loading. However, this practice does not appear to be widely used in the commercial catfish industry when transporting large catfish. Transport Tank Aeration Systems Catfish processing plants are located near larger fish production operations. Close proximity to catfish farms reduces travel time and expense when delivering fish from the ponds to the processing plant. Commercial production ponds and the holding vat facilities of the plant are typically designed to accommodate large, live fish transport trucks. Depending on the capacity of the processing plant, the trucks may range from 1. 36 t to a tractor trailer weighing over 20 t. Catfish are delivered to processing plants at high densities (0.7-1.0 kg/L) to lower transport costs. Trip durations of 1-4 hr are typical. Fish in the transport tanks are supplied with air provided by diesel powered regenerative blowers (Bosworth et al. 2004). Ambient air delivered from the blower is distributed to the tanks via air hoses or plastic tubing. Air flow meters mounted on the outside wall of the transport tank monitors air flow into each compartment. Tubing enters the container through a port and is connected to a weighted, medium to course pore air diffuser device located on the tank bottom. Use of Liquid Oxygen Liquid oxygenation systems are typically used when hauling catfish longer distances, or when stocking lakes and ponds for recreational fishing. Liquid oxygen is released by a low pressure regulator into the transport water as oxygen gas. Side mounted flow meters located on each tank are used to determine the proper flow rate of oxygen into each tank. Oxygen is released from the bottom of the tank through a fine pore diffuser hose configured into a weighted grid or by diffuser rods or stones made of ceramic, plastic, bonded glass, carbon or some other material. Care must be taken not to supersaturate the transport water with oxygen. This could result in excessive oxygen use, and dead or injured fish. A dissolved oxygen meter is used to determine that each tank has the proper dissolved oxygen concentration. Oxygen flow rates must be adjusted for each load of fish, however 1-2 L 0/125 L of hauling water/min may serve as a general guideline (Wurts 1990). A dewar oxygen bottle may weigh 354 kg and hold 127 m3 or 127,426 L of liquid oxygen (Jensen 1990a). One or more dewars are typically fastened to the center, or the rear of the truck bed. Liquid oxygen is more expensive than aeration provided by regenerative blowers and may cost $0. 19/ m3 or more. Water temperatures remain cooler longer with liquid oxygen as opposed to regenera-
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